1. Field of the Invention
The present invention relates to a gas combustion type striking machine for driving a nail into concrete or lumber using a combustion pressure of fuel gas.
2. Related Art
In general, in a gas combustion type striking machine, a piston is provided vertically slidably within a cylinder disposed within a body. A cylindrical-shaped movable sleeve is vertically slidably fitted with an upper outside portion of the cylinder. The movable sleeve is energized downwardly by a spring in such a manner that it is normally situated at its lower position. When the machine is put into its nailing operation, the movable sleeve is moved upward against the spring and is thereby contacted with a cylinder head disposed upwardly of the cylinder, so as to form a closed combustion chamber. Combustion gas existing within the combustion chamber is ignited and combusted explosively to thereby actuate a driver together with the piston. Specifically, using the driver connected to the lower surface side of the piston, a nail supplied to a nose portion disposed downwardly of the cylinder is struck and driven out from the nose portion.
While a trigger for starting the nailing operation of the machine is being pulled, the movable sleeve must be held at its upper position to thereby form a closed combustion chamber. US2010/0176177 discloses a structure in which the movable sleeve is received by a cam made of synthetic resin through a lock-out bar (hold member). The cam is slidably provided in the body and is used to hold the movable sleeve in a combustion chamber sealed state. In order to prevent an activation of the machine in a case that the trigger is pulled first and then the machine is pressed to a workpiece, the cam embraces the lock-out bar to thereby prevent the movable sleeve against movement.
In the above structure, the cam fulfills an important function. However, there is a possibility the cam is deformed due to a heat generated owing to a combustion of mixed gas within the combustion chamber and/or a sliding surface of the cam is damaged by dust or sand generated in a working site.
Also, in a case that a leading end of the machine is struck strongly against the workpiece, the cam can be deformed or damaged.
In view of the above, JP-A-2008-260094 discloses a mechanism in which the lock-out bar is connected to the trigger without using a synthetic resin cam. According to this technology, it is not necessary to pay attention to an influence of heat generated due to the combustion of gas, but a space of the machine corresponding to the cam can be saved to thereby be able to reduce a whole height of the machine.
However, in the structure in which the lock-out bar is connected to the trigger, since a switch mechanism cannot be located in a vicinity of an upper portion of the trigger because the lock-out bar provides an obstacle. Thus, a dead space is generated in the upper portion of the trigger, whereby the space cannot be used effectively.